A body-implantable lead is used with an implantable cardiac device (ICD), such as an implantable pacemaker, a cardioverter, a defibrillator, a cardioverter defibrillator, and the like, to both sense cardiac function and deliver stimulation pulses to a desired tissue location. When the stimulating device is a cardiac pacemaker, for example, the lead, also referred to as a “pacing lead,” connects the pacemaker's electrical circuitry directly with a desired chamber of the heart. One or more electrodes at or near a distal end of the lead placed inside of the heart contact the cardiac tissue at a desired location. The electrode(s) are electrically connected via insulated conductors within the lead to an appropriate connector at a proximal end of the lead. After an implantable lead is transvenously or otherwise implanted at the proper tissue location, the connector at the proximal end of the lead is detachably inserted into an appropriate mating connector of a medical device, such as a pacemaker, thereby electrically coupling the desired tissue location to the electrical circuits within the medical device. The distal tip of the implantable lead is held at a desired tissue location by either active fixation (such as a helix or hook) or passive fixation (such as a tine assembly near the distal electrode).
Body-implantable leads are generally designed to be pliant and flexible as to prevent damage to a patient's vasculature during implantation. Further, it is also desirable to minimize the overall diameter of the lead body, both to increase the pliancy and flexibility of the lead and to make the implantation of such leads as minimally invasive as possible, thus reducing operating room time and recovery time, and minimizing trauma at the introduction site and the likelihood of complications.
Despite the pliant and flexible nature of body-implantable leads, the repeated application of stress can fatigue individual conductors within the leads and eventually result in fracture. Therefore, lead bodies are typically reinforced in regions of expected high stress. For example, a reinforcing polyester cord or a reinforcing conducting coil may be disposed within the interior of a lead and extend the length of the lead. However, such reinforcements may substantially increase the diameter of the lead body and significantly reduce the flexibility of the lead.
The design of internal components for conductor joints of a body-implantable lead may also limit the minimum diameter of a lead body. For example, a conventional joint between an individual cable conductor and an electrode includes a transition member, such as a crimp sleeve, to join together the electrode and the conductor. FIG. 1A illustrates a conventional crimp joint 160 in which a cable conductor 102 is joined to a ring electrode 106 through a crimp sleeve 104. As shown, cable conductor 102 is joined to one end of crimp sleeve 104, and ring electrode 106 is joined to an opposite end of crimp sleeve 104. A conventional body-implantable lead may employ a number of such joints to connect individual conductors to connectors, electrodes, or additional conductors. As shown in FIG. 1B, each crimp joint may have an overall thickness of about 0.015 inches or more, and consequently, the use of transition members, such as crimp sleeves, crimp rings, and crimp slugs, within these conventional joints adds significant volume to the lead body, increasing its outer diameter DOUT, decreasing its inner diameter DIN, and reducing its flexibility. Further, the use of multiple transition members increases the manufacturing costs of the lead.
What is needed, therefore, is a more flexible, pliant body-implantable lead having improved conductor joints, thereby reducing the outer diameter of the lead in comparison to conventional devices.